To optimize the clinical applications of transesophageal echocardiography (TOE), we have compared the contribution of TOE with that of transthoracic echocardiography (TEE). TOE and TTE were performed in 19 outpatients, 17 hospitalized patients and 16 surgical patients (33 males and 19 females, mean age 53.3 +/- 16.8 years). TOE obtained a diagnosis unsuspected from TTE in 12 cases, and additional useful clinical information was obtained by TOE in 15 cases. Surgical treatment was decided on the basis of TOE alone in 8 cases. Patient tolerance of TOE was excellent and no major complications occurred. In conclusion, additional information obtained by TOE was clinically useful in about half of patients (52%), in particular in the diagnosis of cardiogenic embolism and in clinically suspect endocarditis, valvular dysfunction or aortic dissection.